Medical injectors are well known in the prior art, including injectors which have internal drive mechanisms for plunger advancement. Plunger advancement may be utilized to conduct automated reconstitution of a two- or more part medicament and/or to cause automated injection. More specifically, the automation of plunger advancement may be utilized to cause combination of a multiple part (e.g., wet/dry) medicament. In addition, or alternatively, the automated advancement of the plunger may cause a needle to be advanced for injection and/or medicament to be driven through the needle during injection. Such automated action requires a trigger mechanism. Concerns exist over premature or failed trigger activation.